1. just hit the ac button till it says AC off. recirc is your personal preference

2. No. the front defroster is just another vent. defrost works best when you have the AC on so dryer air is blown to reduce moisture on the inside. For ice, it doesnt really matter

3. Doesnt make a diffreence.

if you shift into N... you can shift back into d4 immediately. Just dont let the engine rev up too high in N. Hell you can even shift it into reverse and it wont do anything. (note: do not try this at home. it works on the 6th gens, but i havent tried it on others. dont come to me of you fuck anything up)